FRANKFURT (Reuters) - Microsoft Corp said on Tuesday it had suspended patches to guard against Meltdown and Spectre security threats for some computers running AMD chipsets after complaints by AMD customers that the software updates froze their machines.

Microsoft said in a customer support blog post it had received complaints from AMD customers that their machines stopped loading the Start menu or taskbar after installing Windows operating system security updates.

The issues affect older generations of its chips, AMD said in a statement.

Some complaints on customer support blogs described computers freezing when users attempted to install Microsoft patches on decade-old Athlon X2 chips, for example. A spokesman declined to detail the range of AMD processors affected.

AMD shares fell nearly 4 percent in early U.S. trading on Nasdaq. Last week the stock rose nearly 20 percent as investors speculated AMD could wrest market share from Intel, whose chips are exposed to risks from possible Meltdown and Spectre attacks.

"To prevent AMD customers from getting into an unbootable state, Microsoft will temporarily pause sending the following Windows operating system updates to devices with impacted AMD processors at this time," Microsoft said in its statement.

Microsoft said it was working with AMD to resolve the issues and would resume Windows operating system software updates to affected AMD devices via its Windows Update process as soon as possible. AMD said in its statement it expected Windows updates for its chips to roll out again shortly.

Upon investigation, Microsoft said some AMD chipsets did not conform to technical documentation the chipmaker had provided, preventing Microsoft from successfully patching affected machines.

In its blog post, the software giant said the patches had caused computer screens to freeze up, or have so-called "blue screen errors" on Windows 10, Windows 8.1 and Windows 7.

AMD said last week that differences in its chip designs from rival Intel Corp meant its products were at "zero risk" from the Meltdown flaw but that one variant of the Spectre bug could be resolved by software updates from vendors such as Microsoft.